Triggering circuit



June 13, 1950 J. B. ATwooD ET Al.

TRIGGERING CIRCUIT Filed sept. 26. 1945 H DI l T r/ME BY ATTORNEY Patented June 13, 1950 UNITED STATES' PATENT OFFICE John B. Atwood and Robert E. Schock, Riverhead,

N. Y., assignors to Radio Corporation of America, a corporation of Delaware Application September 26, 19451, SerialNo. 618,760

' A6 Claims. (Cl. Z50-27) l This application discloses an improved translating circuit as used in frequency shift telegraphy systems such as, for example, disclosed in U. S. Application Serial #632,978, filed December 5, 1945. In these signalling systems into remove noise components and fed to a tripping or triggering circuit of the general nature disclosed in Finch U. S. Patent #1,844,950, dated February 16, 1932. A specific triggering circuit may be as illustrated and described in the said U. S. Application Serial #632,978, filed December 5, 1945. The triggering circuit comprises a pair of tubes with their anodes and control grids cross-coupled and arranged and operated so that if current is initiated in one tube it is cutl olf in the other tube and vice versa. Although two tubes are shown with individual evacuated envelopes therefor, it is obvious that these tubes can be replaced by a single tube wherein one evacuated envelope encloses both electrode structures. Double triggering circuits may be used or parallel triggering tubes may be used but for explanation of the present invention a single triggering tube arrangement will suiiice.

The current is tripped from one tube to the other thereof and vice versa in accordance with the magnitude of the pulsating current supplied to the grid of one of the tubes. The triggering circuit squares off the wave form and limits the same to supply at its output potential the magnitude of which shifts sharply between two values in accordance with shifts from mark to space frequency and vice versa. The trigger circuit may indirectly control a tone keyer or printer. In the example given the trigger` circuit operates a stop-start printer through additional circuits not shown. The stop-start printer has been arranged so that it is essential that a mark character be transmitted to the printer in the absence of keying on the transmitter. In the system as explained the signals received are to terminate on mark and start on space.

,1 keying commences.

The transmitter will stop on mark but the possibility exists that a burst of static will pass through the receiver and operate the trigger so that it flips to the space condition. This is undesired since the stopstart printer is arranged to end on a mark character and start on a space character. If this happens the printer mechanism will continuously rotate and may not start in synchronism when Much the same thing may happen when the transmitter goes off the air.

The broad object of the present invention is to improve triggering circuits in this respect. This is done by providing means for restoring the trigit comes to rest in the mark position. The means for accomplishing this is so arranged that the action does not take place until the passing of a suitable time period which is long with respect to the characters being received. When this is so, the` restoring means will not operate between signal characters.

The means for restoring the triggering circuit to a selected condition of stability includes an electron discharge device arranged and operated under certain conditions to set up on one of the tubes a biasing potential which trips the circuit into the condition of stability wanted.

A further object of the present invention is to enhance the tripping action of the triggering circuit to make the same rapid and positive under control of the voltage of varying magnitude representing the signals. This is accomplished by arranging the tube used for the restoring action described briefly above so that in the presence of keying voltages the same assists or expedites or enhances the tripping action.

InA describing our invention in detail reference will be made to the attached drawings wherein Fig. 1 illustrates a trigger circuit including trigger circuit stability restoring means which insures flipping or triggering of the circuit to a particular condition of stability in the event the same is for some reason left in the other condition of stability.

3 signal of varying magnitude appears across the grid bias resistor |03 and on the grid of the cathode follower type amplifying and coupling vacuum tube |04, whose conductivity is controlled by the signal. Resistances 9| and 92 are a voltage divider used to supply a positive voltage on the grid of tube |04 such that its grid-to-cathode potential is near the center of its dynamic range. The net grid-to-cathode voltage will still be negative due to resistor I 08. This increases the alternating current input voltage the tube |04 will handle.

The current through the tube |04 varies in accordance with the keyed input and the potential across the cathode follower resistor |03 varies in a corresponding manner. The potentials of varying magnitude at the high .potential end Viof resistance |08 are applied to the control grid of the tube III) of the triggering circuit and also by condenser |52 to the control grid of the restoring vacuum tube I 50. The anode-of tube `III) is coupled to the grid of tube I4 -by resistance I|'|. The cathode of -tube I|4 is connected to ground by variable resistance III. |Ihe -anode of tube II4 is coupled to the control -grid of `tube I I by resistor II9. The anodes of 'the tubes IIU and I|4 are also coupled by anode impedances |2| and |2| to the positive terminalofa source of direct current potential. Tubes I I0 `and II4 are in the triggering circuit to 'becontrolled and restored to a selected state or condition of stability. Output may be taken between the anode of either tube IIII or I|4 and ground, forexample, as shown by the leads including condenser |25 labeled Output In the absence of keying the -grid of `tube l|50 is maintained slightly positive by -virtue -of voltage supplied from the voltage divider resistances |55 and |56 through resistance |54 `to the said grid. In this condition tube `-I5Il will present `a low impedance plate Vto Acathode circuit. One plate to cathode external shunt circuit -of tube |50 includes the resistance |23, which `with resistances |I`| and |2| forma -potential divider across the direct current source.

In mark condition a positive 4pulse is :applied at |02, appears across |08 -and is applied to the grid of tube I I0 so tube Vl |0 is conductive'and tube I I4 is non-conductive. It'should'bekeptin'mind that the received signals are to terminate Aon mark and start on space. We Ywill-assume, vhowever, that static or other disturbance has tripped the circuit so that tube ||0 is vcut 01T and tube ||4 is conductive. Then lthere is a vlarge potential drop across resistor |23,'since rtube |f|0 is cut' oi thus raising the potential at its plate which is applied to the voltage divider including resistors III, |2|- and |23, to produce the positive voltage required for the grid of tube |I4. However, tube |50 has its output impedance across this resistor |23 and since its grid is made lslightly positive `by resistance |54, and potential -divider resistances |55 and |55, in the 'absence of keying, tube |50 presents alow impedance. Current flows in tube |50 and resistances II'I and |2|, and the potential on the grid of tube II4 'is reduced by the low impedance path through tube |50 and the trigger Acircuit flips to its condition of stability at mark frequency, i. e., tube I I4 is made non-conductive and tube I I0 is conductive.

After keying signals have `been applied for some time, tube 50 develops a negative bias 'about which the keying pulses are centered. When keying stops, the resulting action depends upon `Whether the keying stops on markor space. If

the keying stops on mark, the grid of tube |50 will be slightly positive and in the normal condition, ready for keying to recommence. If the keying stops on space tube |50 becomes cut off due to the negative bias built up on its grid and held by the time constant circuit including condenser |52 and resistance |54. The time constant of this circuit is long relative to the keying speed. This bias will gradually leak oif and the grid of tube |50 will become slightly positive, `thereby conditioning tube |50 to restore the trigger circuit if it is not in the proper state of stability.

This tube |50 performs another function between the time 'the keying starts and cutoff bias is built up on its grid. It helps throw the trigger as controlled by mark and space voltages by the following action.

In the invention as described the rst thing that happens when keying commences is ap pearance-of a negative pulse representing space across resistor |08 which is -coupled to the vgrid of `tube |50 through 'condenser 52. This is of large Aenough amplitude to cut oif tube |50. This in turn applies a positive pulse -to the grid of tube I-I4 (the drop across resistance |23) which Will 4help throw the trigger circuit. The negative applied pulse is also and simultaneously applied to the grid of tube III, which is :the normal way the trigger fis tripped when tube -I 5U is nallyfcut off by the bias supplied 'by the keying.

During operation, then, vwhen 4the trigger circuit is on the -mark side the triode -I I0 is 'conducting andthe triode I I-4 is non-conducting, All the code groups of the vtype printer' this unit is arrangedito receive,-end iin astop character which is a mark character. Therefore, when keying stops, the trigger keyer control of the frequency shift keying unit is normally left on the mark side, i. e., tube -I'5I0 conducts. -It 'would be possible, however, for a pulse of Inoise -to trip the trigger to the space side, i. e., tube |.I4 conducts, and leave it there. In such an event tube |50 restores the circuit to mark side byfdrawing current through the resistor |II connected to the triode I4 grid Whichresults in a lowering of the potential on that grid 4and "hence la lowering of the conduction of that Vtriode |14 to the point Where trigger action vtakes place and the -tube I I4 triggers to complete vnon-conduction and the triode IIIl to conduction.

The rstfcharacter of each printer code :group is a'start character which is'always a spacechari acter. This start or space character appears as a 'negative pulse across the vresistor |108, just -referred to, and is of suchamplitude that its action on the -grid of tube |50 through the connecting condenser |52 renders `tube |50 non-conducting for the 'duration of the space character. This leaves 'the trigger free to react to the less positive pulse `fed 'to the triode I-III grid. This pulse on thegrido'f tube I l0 causes 4it to trigger tothe nonconducting 4or Aspace'condition and of course the triode 1I I4 to conduction. Any mark character which follows, being of more positive polarity across the resistor |08, is partially rectified on the grid of tube |50 so that tube |50 is conducting on this mark character. Being conducting, it places a less positive vpulse on the triode I'-|`4 grid which aids the more positive Ymark pulse fon the ytriode f'I'I'Il grid vin triggering lto lmark condition.` Therefore while keying -is in'progress, tube |50 aids in keying the trigger. When keying stops, ending as has been stated in a mark character, this 'final positive character appearing 'on the grid of tubev lsu is partiauy rectined at this an additional function.` The keyed wave at Ill2,r

and w8 may not be of rectangular wave form. The leading and trailing edges may .slope as shown in Fig. 2. ,The resulting mark and space time intervals may then be unequal as illustrated in Figs. 3 and 4 unless the reversals take place at the proper timey as set byvtripping tube bias and signal pulse magnitude at which tripping takes place. The variableresistancelll is a means for adjusting the pointat which the tripping action takes place. In other words, adjustment of l l varies the bias on the grid of I I0 which is overcome by the potential at |06 to set the tripping action in motion. In practice the magnitude of signal pulse at which the trigger is tripped to the mark condition may not be equal to the signal potential at which the trigger trips to the space condition. For example, the trigger may trip to mark when the signal magnitude reaches a value represented at a Fig. 2, and trip back to space when the signal magnitude falls to a value represented at 5, In this case-mark is longer than space, as shown in Fig. 3. When the tripping action .takes place at c and 41, Fig. 2, space is longer than mark, as shown in Fig. 4. In practice, adjustment is such that mark and space are made equal.

What is claimed is:

l. 'In a signalling system in combination, a triggering circuit comprising a pair of electrode structures having electrodes including an anode, a grid and a cathode, impedances cross-coupling the grid and anode electrodes of said structures and coupling said electrodes to direct current potential sources such that when current starts to flow in one structure the bias on the grid of the other structure relative to its cathode is reduced to reduce current therein and vice versa, and current is tripped through one structure and cut ofi in the other structure and vice versa, a source or pulse energy of varying magnitude coupled to the grid of one structure to control the current through the structures, said pulse energy representing signals arranged to terminate in the same character so that a first one of said pair of structures is normally left in a conductive condition and the second structure is left in a non-conductive condition, and means for restoring said conditions in the event static or other disturbance leaves said first structure nonconductive and said second structure conductive, comprising a resistance between the grid of the second structure and its cathode, an additional tube having input electrodes which are normally biased so the additional tube is conductive and having output electrodes connected across said resistance, and means for applying said pulse energy to the input electrodes of said additional tube.

2. In combination, a circuit comprising two electrode structures each having an anode, a cathode and a control grid, a resistance coupling the anode of each structure to the grid 0f the other structure, additional resistances coupling the electrodes to a source of potential such that 6.. when current starts to iiow in a first structure the bias on'the grid of the second structure relative to its cathode is reduced to reduce current therein' and current is tripped through said first structure and cut off in the second structure and vice versa, a third resistance between the grid of said second structure and ground, a variable resistance between the cathode of said second structure and ground, a source of pulse energy of varying magnitude coupled to an electrode of one of said structures to control the current flow therethrough, said pulse energy representing signals which terminate in a manner to cut off current in said second structure, and means for restoring such terminal condition in the event static or other disturbance has altered the same including a third tube .having output electrodesv including an anode and a grounded cathode and having input electrodes including said grounded cathodey coupled to said pulse energy source, means for applying a slightly positive biasing potential to said input electrodes, and a connection between the anode of said third tube and the control grid of said second structure.

3. In telegraphy apparatus, in combination, a circuit comprising two tubes each having electrodes including a cathode, an anode, and a grid; impedances cross-coupling thegrid and anode electrodes of said tubes and coupling said electrodes to direct current potential sources such that when current starts to ow in a first tube the bias on the grid of the second tube relative to its cathode is reduced toreduce current therein, so that current is tripped through said first tube and cut off in said second tube, and vice versa; biasing circuits for the grids of both tubes including a resistor between the grid and cathode of said second tube; an output circuit coupled to one of said tubes; a source of pulse energy of varying magnitude coupled to the control grid of said rst tube to control the current ow therethrough, said pulse energy having a wave shape representing signals which terminate in a manner to cut ol current in said second tube; and means for restoring such terminal condition in the event static or other disturbance has altered the same, said means including a third tube having output electrodes. and having input electrodes coupled to said source of pulse energy; means for applying a slightly positive biasing potential to the input electrodes of said third tube; output circuit connections for said third tube including in series its output electrodes, the impedance connected between the grid of said second tube and the anode of said first tube, and a source of direct current potential; and means connecting the output electrodes of said third tube in shunt to said resistor.

4. In combination, a triggering circuit comprising two tubes, each having an anode, a cathode, and a control grid; a resistance coupling the anode of each tube to the grid of the other tube; connections for applying charging potentials to the anodes of said tubes and biasing potentials to the grids of said tubes, such that when current starts to flow in one tube, the bias on the grid of the other tube is reduced to reduce current therein and current is tripped through said one tube and cut on in the other tube, and vice versa; a resistance between the grid of each of the tubes and ground; means for adjusting the bias on the grids of the tubes to vary the point at which tripping action takes place, including a variable resistance in the common connection between the cathodes of said tubes and ground; a source of pulse energy of uvarying magnitudecoupled to the control .grid of a first .one of said tubes to .control lthe current .now therethrough, said pulse energy representing .signals which terminate in a manner .to cut 01T current in the second vone of said tubes; and means for restoring .such tenminai .condition in the event .static or other disturbance :has altered .the same, including a third tube having output electrodes comprising Aan .anode and a vgrounded cathode and having input electrodes including said grounded cathode coupled to said pulse energy source; means for applying a slightly positive biasing potential to the input electrodes of said third tube; a connection between the anode of said third Itube .and the control grid of said second tube.; andan output circuit ccu-plod to one of said first two tubes.

5. 'In telegraphy Asignalling apparatus, a .circuit comprising two tubes, each having electrodes including a cathode, an anode, and a grid; connections cross-coupling the anodes and grids; connections for applying .charging potentials to the anodes and 'bias to the grids, .such ythat when current starts to flow in one tube the bias on the grid of the other tube is reduced to reduce current therein so that current is tripped through said one tube and cut off in the other tube, Aand vice versa; a first resistance in the coupling between the anode of one tube and the grid of the other tube; a second resistance between the grid of the other tube and ground; a Asource of lpulse energy .the magnitude of which varies relative to ground; means coupling said source lto lthe control grid of said one tube to control the current therethrough; a common adjustable resistance between the cathodes of both said tubes and ground; a third tube having output electrodes and having input electrodes, including a control grid, coupled to said pulse energy source; means for applying a :slightly positive biasing potential to said control grid of said third tube; and means coimecting the output electrodes of said third tube in shunt to said second resistance.

6. In combination, a circuit comprising two tubes `each having electrodes including a .cathode, an anode, and a grid; a resistance coupling the .anode of each tube to the grid .of 'the other tube; connections for applying charging potentialsto .theanodes of said tubes and .biasing potentials to the grids of such tubes, such that when current starts to ow in one tube the vbias on the grid of the other tube is reduced to reduce current therein, and current is tripped through said one tube and `cut .off in the other, and vice versa; a third resistance between the cathode and grid of .said .other tube; a third tube having input electrodes including a grid and also output electrodes; means for .applying a slightly positive biasing potential to .said .input electrodes; means connecting the routput electrodes of said third tube in vshunt to said third resistance; a fourth tube having input :electrodes including a cathode excited by '.pulse energy representing signals and having :an .output circuit including a resistance connected between its cathode and ground; means connecting said fourth tube to a source Kof energy for energizing Athe same; a coupling between the cathode of the fourth tube and the grid ofthe third tube and the grid of said one of said first two tubes; andan output circuit coupled to an output electrode of one of said iirst two tubes.

JOHN B. ATWOOD. ROBERT E. SCHOCK.

REFERENCES CITED LThe following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,717,624 Ranger June 18, 1929 1,979,484 Mathes Nov. 6, 1934 2,211,750 Humby et al. Aug. 20, 1940 2,266,401 Reeves Dec. 16, 1941 OTHER REFERENCES Journal of Scientific Instruments, v01. 15, 1938, A Therniionic Trigger. by Schmitt, pages 24-26. Copy in Scientific Library. 

